Add dev container configuration

[dblnz]

The following dev container configuration can be found in the .devcontainer directory.
It contains:

• devcontainer.json a configuration file for the Dev container that puts everything toghether
• create_env.sh script that is run on the host machine and creates a .devcontainer/.env file that contains the necessary group info for the container image build phase
• Dockerfile.base config for a base container image that is pre-built by using the .github/workflows/CreateDevcontainerImage.yml action that is automatically triggered when a change is detected for Dockerfile.base or the workflow configuration.
• Dockerfile config that uses the pre-build image as a base image, creates a group with the same GID of the device being passed to the docker container and adds the user to that group

Note: The reason why the environment file generation is needed is because in order to access the device (/dev/kvm) inside the container, the user needs to belong to the correct group, so the group is created at image build time.